rgw: migrate to using non-deprecated class call functions

Update the Rados Gateway driver to utilize the new trait-based class
method interface. This replaces legacy string-based exec() calls with
the typesafe template-based alternatives.

Key Changes:

Updated reset_stats in buckets.cc to use cls::user::method::reset_user_stats2.

Updated RGWRadosBILogTrimCR in rgw_cr_rados.cc to use cls::rgw::method::bi_log_trim.

This change ensures that RGW operations are correctly categorized as
reads or writes at compile-time, aligning with the broader effort to
improve RADOS class method safety and OSD routing efficiency.

Signed-off-by: Alex Ainscow <aainscow@uk.ibm.com>